The present invention relates generally to an apparatus for providing damping, and more specifically to an apparatus that provides damping using direct shear of a viscous fluid.
Since the onset of space exploration and satellite usage there has been a need to control deployments of spacecraft mounted appendages such as antennas, solar arrays, and booms. Controlling such deployments can reduce the loads of appendage spacecraft primary structures as well as momentum compensation demands on the spacecraft attitude control system.
Generally, the appendage deployments are controlled by passive rotary dampers. These rotary dampers normally are attached to a spring-loaded device or motor in a parallel fashion. The rotary dampers provide velocity damping to the system by either restricting fluid flow across an orifice or by electro-magnetically removing energy from the system by generating eddy currents internal to the spring-loaded device.
However, such rotary dampers have a propensity to leak viscous fluid from shaft seals and have inconsistent performance due to a lack of thermal compensation. In addition, these rotary dampers require additional power for heaters as well as complicated switching electronics to compensate for a wide range of damper performance over different temperatures.
In addition, the above-described dampers that generate eddy currents require a gear reduction train to derive practical damping characteristics. This gear reduction train adds a high amount of complexity, weight and cost as well as reduced reliability.
Therefore, what is needed is a rotary damper that can control appendage deployment at a low level of complexity and cost and in a reliable manner.
In view of the above, the present invention provides a rotary damper for providing control of appendage deployment. The rotary damper includes a stationary member, a rotating member provided within the stationary member, a gap defined between the rotating member and the stationary member, and a viscous fluid provided in the gap. The viscous fluid has a shear that provides a velocity damping within the gap. A differential growth generated in the gap as a result of different coefficients of thermal expansion varies the width of the gap and compensates for temperature damping variation. The rotary damper further includes a linear bellows that defines a viscous fluid chamber and provides fluid thermal compensation. A rotary bellows is provided on the stationary member and on the central shaft for preventing viscous fluid leakage.
In a first species of the rotary damper, the stationary member and the rotating member comprises a drum damper in which the stationary member constitutes a stationary housing having a first coefficient of thermal expansion and the rotating member comprises a rotating cylinder having a second coefficient of thermal expansion.
In a second species of the rotary damper, the stationary member comprises a stationary housing and a plurality of stationary discs, and the rotating member comprises a plurality of rotating discs interspersed between the plurality of stationary discs in an alternating configuration. The rotating discs and stationary discs have the second coefficient of thermal expansion while the stationary housing has the first coefficient of thermal expansion.
The present invention consequently provides temperature damping compensation and thermal compensation without the complexities and costs of a gear reduction train.